well, looks like everything is pretty tight. I may shim the rear axle to see if it helps, but i am just thinking i may leave it the way it is and forget about it. thanks for all the insight and the greetings though!

ok, drove quite a bit in 4wd this past weekend. there is definitly a problem with the transfer case. I get a CRAZY vibration on decel from anything above like 20mph when the thing is in 4wd and the hubs are locked. with it in 2wd and th ehubs locked it vibrates, but i have decided it is a livable amount. I will probably drive it for a while like this avoiding 4wd at higher speeds untill i get a chance to take the transfer case back apart..

My truck isn't stock, and I've had it long enough to try lots of things.
Driveline vibrations certainly are speed specific and probably what you are dealing with. I doubt your diff setup is bad since you drove it so far already.

Step 1 verify driveshaft phasing. The Y parts of the yolks should match. So the ones welded to the driveshaft and slip yolk should be exactly the same. I have a feeling your FRONT problem is driveshaft phasing going by how severe it seems. It is easy to be off a tooth on the driveshaft and it "looks" right until you put the shaft on the ground.

While you have it down on the ground, go have it balanced. maybe you knocked off a weight on a rock?

Still working on the front...The only thing that can be wrong with the t-case is wobbly output bearings at the t-case. I kinda doubt this because if the bearings are this beat, they leak like the Exxon Valdez. EZ to check. just lever on them up and down. On my mini truck, it is easy to change only the front output.

Uncle Ben already described the angles thing. Basically, with single u-joints on each end, the flanges need to be parallel for smooth operation. Remember, with leaf springs there is some axle wrap under "normal" driving so you tend to "pre-tilt" the rear down about 1/2 to a degree or so. Oon the front, caster is WAY more important for day-to-day use.
Get the caster where you want it first. We'll fix your driveline in a second.

Next up, the "double cardan" you've seen 'em. 2 u-joints back-to-back. UB described these too. Forget the physics arguments. Here is how it works. Point the rear diff flange directly at the t-case flange. Put the double cardan at the t-case end. Single U is all you need at the bottom.

OK. How do you decide which way to shim? Down for parallel? or up straight at the t-case flange for a double cardan? Well, which way is closer? Can you afford to have a double cardan driveshaft built? Want to get the nose of your diff out of the rocks and the driveshaft angles reduced? Don't care that the fill hole is now useless on the diff and the anal retentive will tell you your pinion bearing won't get lubedt? shim the nose UP and get the double cardan shaft under there.

Decision made? Uncle Ben also described how shims are frowned upon. Yeah. U-bolts end up too short on 1 side, e-brake cable runs into the leaves, shims split and spit out....sucks. Here is whatcha do. Do the math as best you can and buy shims as close as you can calculate and estimate. get steel shims only. install and TEST. when you find a shim you like, weld them to your perches. the BETTER OPTION: drop the axle. cut off the original spring hangers and weld on new ones. Rotate the axle housing to the new, optimized and tested angle. now when you bolt it up everything fits right and, "Stock". Cutting and welding hangers isn't a big deal really and the result is much better than an angled shim.

On the front: Run the double cardan. even if you have non-parallel flanges, the vibration won't be as bad.

ok, i've decided that the rear is fine after lots of driving like you guys said above. totally livable amount of vibration for me... and like spanky said above th ediff seems to be living fine.

so, i pulled the front ds just now to see if th etransfer case output flange was not wobbly and the nut was tight.. they are both fine... as is the pinion flange in th efront. all tight. anyways.. that basically leaves the front driveshaft. It is pretty solid, no weights have been thrown, and after lots of driving around here in the past week in slushy conditions in and out of 4wd with the front hubs locked i have noticed it only vibrates when th ehubs are locked and it is in 4wd and there is slack in the driveline. with just the hubs locked and the driveshaft freewheeling it never vibrates (not even at 80mph).

So, two questions.

one, does it matter if the slip yoke is near the transfer case or near the diff? it was set up near the diff when i got it, so thats how i put it back.

Two, how much slop in the slip yoke is ok? it has a bit of slop (like wiggles in the direction if you were to try and fold it in half) but i dont know if it is too much. it is less than the rear. I am about to go for a drive and see if it makes the same vibraton in 4wd with the driveshaft removed. hopefully that will certianly rule out the transfer case.

also, the shaft is "in phase" as far as i can tell with it out and looking straight down the flanges.